1. Field of the Invention
The present invention generally relates to speech and speaker recognition and, more particularly, to text independent speaker recognition, which may thus include consistency checks of the recognition process, particularly suitable for continuous security and access control and which is transparent to one or more users and provides enhanced resolution of ambiguities between recognizable commands.
2. Description of the Prior Art
Many electronic devices require input from a user in order to convey to the device particular information required to determine or perform a desired function or, in a trivially simple case, when a desired function is to be performed as would be indicated by, for example, activation of an on/off switch. When multiple different inputs are possible, a keyboard comprising an array of two or more switches has been the input device of choice in recent years.
However, keyboards of any type have inherent disadvantages. Most evidently, keyboards include a plurality of distributed actuable areas, each generally including moving parts subject to wear and damage and which must be sized to be actuated by a portion of the body unless a stylus or other separate mechanical expedient is employed. Accordingly, in many types of devices, such as input panels for security systems and electronic calculators, the size of the device is often determined by the dimensions of the keypad rather than the electronic contents of the housing. Additionally, numerous keystrokes may be required (e.g. to specify an operation, enter a security code, personal identification number (PIN), etc.) which slows operation and increases the possibility that erroneous actuation may occur.
Perhaps more importantly, use of a keyboard inherently requires knowledge of particular keystrokes or combinations thereof which are associated with information (e.g. instructions or data) which must be input. For example, a combination of numbers for actuation of a lock for secured areas of a building or a vehicle requires the authorized user to remember the number sequence as well as correctly actuating corresponding switches in sequence to control initiation of a desired function. Therefore, use of a keyboard or other manually manipulated input structure requires action which is not optimally natural or expeditious for the user. Further, for security systems in particular, the security resides in the limitation of knowledge of a keystroke sequence and not in the security system itself since a security system relying upon correct keypad entry cannot identify the individual person who is currently actuating the keys.
In an effort to provide a more naturally usable, convenient and rapid interface and to increase the capabilities thereof, numerous approaches to voice or sound detection and recognition systems have been proposed and implemented with some degree of success. However, some aspects of known voice actuated systems do not significantly improve over keyboards in regard to transparency to a user or continued security once access is initially granted.
For example, a simple voice actuated system which relies on template matching of the acoustical content of an utterance to allow access to a system (e.g. a file or command set existing on a data processing system) generally requires a particular word or phrase to be input for each enrolled (e.g. authorized) user. (Thus, such a system relying on a particular utterance is referred to as being text dependent or text prompted when the text of an utterance is prompted by the recognizer.) Assuming a correct match is found among enrolled users, no further check of the authorization of the user can be made without requiring the particular recognizable utterance to be repeated during an interruption of usage of the system. Thus, without such interruptions of use, such as by periodically prompting the user for a particular utterance, and the consequent inconvenience, once access is granted, subsequent unauthorized use may not be prevented as might occur, for example, if an authorized user were to momentarily leave a terminal without logging off. It should also be recognized that the requirement for the utterance to be confined to particular text is conceptually identical to the use of a predetermined key sequence such as a personal identification number (PIN) entered on a keypad and, moreover, the utterance cannot be protected from interception by others as readily as a key actuation sequence can be adequately shielded from view. Further, simultaneous authorizations may not be accommodated, much less speech recognition ambiguities resolved in text-dependent systems even though the incidence of such ambiguities would be expected to increase as the population of simultaneously authorized speakers increases. Further, text dependent and text prompted systems can be defeated by mechanical or electrical reproduction of speech. In contrast, continuous checks of speech, making attempts to compromise security difficult together with increasing the difficulty of carrying out any unauthorized use to the point of near impossibility would require text independence.
Indeed, when the speaker recognition is performed in parallel with another process, the command or answers produced by the user must be consistent with the procedure. For example, if the speaker recognition is performed while the user interacts with an operator of a call center, as will be later described, the ability to maintain a coherent discussion is a natural way to check that the voice is not the product of reproduction or synthesis. With automatic systems, answers to questions and relevance of the command fulfill the same role. In a more elaborate case, the system could ask questions personal to the user at some random moment in order to check the answer and thus authenticate the process. On the other hand, when the speaker recognition is text independent, all of the interaction is monitored to verify the user while authenticating the answers.
In summary, dependency of speech recognition on specific text is a limitation on the level of security that can be provided as well as the functionality of the entity to which speaker recognition is applied, whether for security purposes or not. More importantly, however, the obtrusiveness attendant upon text dependency effectively prevents speaker recognition from being used in many applications in which it would yield substantial convenience. For example, once a speaker (or even a combination of speakers) is identified, the identification can be used to retrieve a name and personal information such as preferences, history of previous activity such as commands can be retrieved and used to automatically control a device or system, possibly in an adaptive manner.
Such controls could range from automatic seat and steering wheel adjustments in an automobile to establishing communication links and calling applications commonly used by a particular authorized user when the user logs onto the system. Similarly, text independent speaker recognition would be useful in shared voice dialing systems (corporate voice dialing) and voice controlled answering machines in which the identification of an enrolled speaker could be used to retrieve lists of enrolled names to be dialed or from whom messages should be retrieved (particularly in the case where different speakers might use the same name or word to refer to different people) and other shared xe2x80x9cdiscourse managementxe2x80x9darrangements such as voice controlled e-mail, calendars, address books, and the like.
Text independence would also allow the speaker recognition function to be carried out in parallel with other functions in a manner transparent to a user and for a plurality of concurrent users at differing access levels without requiring interruption for new commands or identification of a user whenever a new user is encountered. Thus, access control or personalization can be carried out on a substantially continuous basis without any user detectable interference with other operations or system functionality even though some processing overhead would, of course, be necessary. Moreover, text independence of speaker identification supplies additional information which could be used to accommodate particular preferred utterances of each enrolled user and to improve resolution of ambiguity of command understanding as well as presenting the possibility of coherence checks to validate the recognition process and avoid compromise of the system through use of mechanical or electrical sound reproduction.
It is therefore an object of the present invention to provide a speaker recognition system which is text independent and transparent to any authorized user.
It is another object of the invention to provide a speaker recognition system which improves command understanding ambiguity resolution.
It is a further object of the invention to provide a speaker verification system which can accommodate a plurality of speakers concurrently and maintain access control for one or more users during use without interruption of such use.
It is a further object of the invention to provide an access authorization control system which can concurrently provide different levels of access authorization to each of a plurality of concurrent users.
It is a further object of the invention to provide a text independent system of speaker identification and verification which can be directly used in call center types of environments to simplify access to a customer file and in which the verification is used as a secondary system to accept the customer""s commands or requests.
In order to accomplish these and other objects of the invention, a method and apparatus for text independent speaker recognition is provided comprising Arrangements for performing the steps of sampling overlapping frames of a speech signal, computing a feature vector for each said frame of the speech signal, comparing each feature vector with vector parameters and variances stored in a codebook corresponding to an enrolled speaker, accumulating the number of frames for which the corresponding feature vector corresponds to vector parameters and variances in a codebook, and identifying an enrolled speaker or detecting a new speaker in response to results of the accumulating step or the comparing step, respectively.